Staircase



FIG. 1 is a front perspective view of a staircase showing our new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a top view thereof; and,

FIG. 6 is a bottom view thereof.

The broken lines in the Figures show portions of the staircase or environment that form no part of the claimed design.

The dot-dash lines in the Figures show unclaimed boundaries that form no part of the claimed design.

The oblique shade lines in the Figures show transparency and not surface ornamentation. 

CLAIM The ornamental design for a staircase, as shown and described. 